Rust's support for cross compilation, both in the compiler and the tooling (cargo, multirust/rustup) is amazing. Last week I was working on a hardened system project. It involved building a system consisting of just a kernel and a single process. At first I was going to target a unikernel, so I pulled the "x86_64-rumprun-netbsd" target, read some docs on rumprun, and in about 30 minutes I had a Rust project running as a unikernel, all well supported by Rust and its tooling.

For various reasons I had to drop the unikernel and switch to Linux combined with the program (I set the program as init, so Linux boots, runs the program, and that's that). That was super easy as well. I grabbed "x86_64-unknown-linux-musl", and the Rust program runs like a champ as the init process on this Linux "system" with no libraries to speak of.

I'm also immensely happy that I added the .cargo/config "target" option to Cargo's code. "cargo build" is much nicer than "cargo build --target=name_of_the_target_which_I_will_never_remember_x86". Cargo's code was fairly simple to dive into, and Rust's team has made the contribution process smooth and bulletproof (thanks to all their Github bots and unit/integration tests). I think that pull request was resolved in about a week (mostly due to waiting for the team to meet and confirm that they wanted to add that flag to the config file).

> Rust has already been ported to Emscripten (at least twice), but the code has not yet fully landed. This summer it’s happening though: Rust + Emscripten. Rust on the Web. Rust everywhere.

I've been following the various RFCs and PRs for emscripten support for awhile now, and it's been cool to see some slow but steady progress. It's very nice to hear the Rust team acknowledge that they are actively moving towards making the web a first class target in the near future.

> Rust is uniquely-positioned to be the most powerful and usable wasm-targetting language for the immediate future. The same properties that make Rust so portable to real hardware makes it nearly trivial to port Rust to wasm.

As a web developer I couldn't be more excited to be using Rust right now. There's been a good amount of movement among JavaScript developers toward type systems and more explicit typing in JavaScript code. I find it's a much nicer development experience to have sane guarantees about the types in your JS code. I see Rust as the big next step for the web—a language that is still a pleasure to develop in, but with excellent static typing and tight, targeted builds without the bloat and buildup I'm accustomed to seeing with current transpile-to-JS strategies.

> I see Rust as the big next step for the web—a language that is still a pleasure to develop in, but with excellent static typing and tight, targeted builds without the bloat and buildup I'm accustomed to seeing with current transpile-to-JS strategies.

I think this will depend on the output size of the compiled file. I've always gotten very large js files out of emscripten, which are fine for games or media decoders, but would be undesirable for (e.g.) a vdom implementation that's part of a larger framework.

Both Rust and emscripten do produce notably large output. On the Rust side it's true that the emscripten port won't use jemalloc, but instead the emscripten malloc (which presumably is better tuned for its environment). Also the wasm format's main design goal is to reduce binary size.

Agreed. I'm moderately optimistic though - statically-linked Rust binaries have always tended to be on the chunky side, but AIUI a lot of that footprint is jemalloc, which I'd hope wouldn't be included in an Emscripten build.

> There's been a good amount of movement among JavaScript developers toward type systems and more explicit typing in JavaScript code.

> There's been a good amount of movement among JavaScript developers toward type systems and more explicit typing in JavaScript code.

This is key to me. I'm not really interested in bolt-on additions or slight variations to JavaScript that leave me still grating against the edges of the language. Whether it's rust or something else, I want to use a language that's well designed, or at least consistent in the browser.

> I see Rust as the big next step for the web—a language that is still a pleasure to develop in, but with excellent static typing and tight, targeted builds without the bloat and buildup I'm accustomed to seeing with current transpile-to-JS strategies.

Maybe this will happen but it won't be through Emscripten. Emscripten is cool and all but it produces really poor code size-wise. Maybe if you lack JavaScript expertise you'll use this as a stop-gap but for a production system that needs scale I can't see it happening.

Now maybe if it can be compiled into the Web Assembly intermedia? That seems like a good route to take.

That's addressed in the article. The LLVM backend is on the way and Rust will be able to take advantage of it relatively easily, it seems. Emscripten is more of an intermediate step to get Rust working on the web in the meantime—I doubt it's going to be the long-term solution for Rust on the web.

2. The article says "for technical reasons, glibc cannot be fully statically linked" . Did this apply to Golang too? Is Golang using musl too on Linux? If no, why not / what is their strategy/tooling to produce static binaries?

2. From my own biased observation/reading of Golang writings and usage of Golang binaries, I feel static-by-default is hugely appreciated, for the portability. Did Rust consider it?

1. I'm not certain on the precise binary layouts etc, but I believe the answer is "yes, except Go binaries can't be stripped". In terms of practical usage, they'll run on the same machines.

2. This is a long one.

The statement you've quoted is false. However, it's both a) a common misunderstanding and b) a sort-of-ok simplification (the full story is much more involved). I'd personally alter it to say "it is technically challenging to statically link glibc". You can read more about the whole musl Rust origin story at [0]. The 'problem' with glibc is that it uses NSS, a feature that allows you to dynamically load libraries installed on the system to let you change how some libc functions work (if neither you nor your libraries use these functions, static linking with glibc works). For example, musl will look up users from /etc/password, whereas with glibc an admin can install an LDAP library, change a config file and all programs using glibc will magically use LDAP. But, you can disable NSS in glibc at compile time [1], which then allows you to truly statically compile with glibc.

Go is interesting because doesn't use libc at all (when using the standard compiler)...except when doing some network things that NSS is useful for, when it does link against it. People who want totally static binaries pass a few additional flags to say "don't use NSS, use the Go implementation of these features"...and you then end up with bugs like [2].

3. Yes [3], but you lose (by default) a) the ability to use shared libraries from the system, b) NSS. Given that one angle Rust is pushed from is "C/C++ replacement", not being able to link to system libraries without using arguably cryptic command line arguments would be a bit sad. But I'm ambivalent about this.

> Go is interesting because doesn't use libc at all (when using the standard compiler)...except when doing some network things that NSS is useful for, when it does link against it. People who want totally static binaries pass a few additional flags to say "don't use NSS, use the Go implementation of these features"...and you then end up with bugs like [2].

Oh god, I completely forgot about that bug. For what it's worth, the technical reasons why Docker had to be linked statically are no longer valid and so it should be able to fix that issue. Unfortunately, "os/user" is lacking some things we need within runC and Docker.

Docker is available statically linked now yes, and it works fine. Although that issue is still open, you have to use dynamically linked version if you want to use these features. Docker is not required as a trampoline any more.

I'm sure I'm not the only person who works in an environment where there are many thousands of Linux and Unix boxes, and they are all configured to use LDAP for /etc/passwd, /etc/group, etc. If a program uses NSS, it will just work; if it tries to read /etc/passwd for itself, it won't find most of the users (including likely the user it is running as).

One solution might be if the statically-linked program included an nscd client, since most people using NSS+LDAP will be using nscd for caching.

Why can't nscd support those other NSS modules too? (Even if it doesn't work with them at present, could it not be extended to do so?)

Rather than having NSS plugins loaded into every process which needs name services, why not centralise all name services in a daemon (whether nscd or sssd or something else)? Then client processes don't need to actually load the NSS code into their own address space, they can just speak a simple protocol over IPC to access this functionality out-of-process.

Rust chooses to call jemalloc for allocations by default[0], as it is generally faster than the system allocators, especially as we can go beyond the plain malloc/free interface. This choice is independent of the libc used, which Rust mainly uses for syscalls.

I'm hoping this follows the "functional" paradigm, where a compile command is invoked, and the compilation result depends solely on the arguments of the command, and not on configuration files and such. This makes it much easier to script things, to use alternative build systems, and, in general, to keep things predictable.

I'm saying this because I'm detecting a trend in a different direction, where tools are making things more confusing instead of more clear.

Rustup manages installing rustc, cargo, and toolchains: it's not what you use to compile. Cargo does have a single Cargo.toml that manages per-project config stuff. But keeping it in a file is part of repeatable builds...

There are a few key arguments for keeping them separate from my perspective:

First, they have distinct audiences. Cargo is a tool for building Rust programs no matter how you obtained the compiler. rustup is a tool fundamentally for installing the official Rust binaries. So if Cargo contained rustup, that would be a large chunk of features that have an very unclear role when Cargo is distributed by Linux distributions, and would probably need to simply be compiled out.

That last point about compiling out rustup also points to the fact that Cargo's and rustup's features are completely orthogonal. There's no technical reason to combine them.

Of course, the practical reason to combine them is that one tool is conceptually simpler than two. Even I have found myself accidentally typing `cargo update nightly`, `rustup build`, etc.

Finally, releases of Cargo today are paired with releases of rustc. Distributing the Rust installer with Cargo would necessarily change that relationship. That is, there would be one global Cargo that is used with every revision of rustc. This isn't necessarily a bad way to arrange the tools, but it is a big change from today that would require significant effort to move to.

Cargo cannot control versioning of Cargo, or at least, an external tool that handles versioning everything seems conceptually cleaner to me than making Cargo version both Cargo and rustc. It's also pretty similar to tools in other ecosystems.

There is ongoing discussion about possibly adding configuration to Cargo packages with a minimum rustc version for the package; the details have not all been worked through yet.

Yes coming from nixos, this "foo install me tools; bar build me project" ideom is quite primitive. I have an long-open RFC that I hope will get cross-compilation working the right way https://github.com/rust-lang/rfcs/pull/1133.

That said RustUP is still a fine easy way to get compilers builds as opposed to standard library builds. I view it as convenient duck-tape analogous to Haskell's stack in that regard.

> I'm saying this because I'm detecting a trend in a different direction, where tools are making things more confusing instead of more clear.

Rust tools in particular, or tools in general? Just curious; the ease of use of Cargo is one of the things that initially drew me to Rust, and rustup seems pretty cool too (just used it to install Rust nightly on a new machine) but I have not done any serious work with Rust yet.

In the beginning, there was multirust. This was a bash script, or rather, a set of them, I guess. It didn't really work on Windows, though, being a bash script.

Then came multirust-rs. We already have a programming language that we like to write that supports the platforms Rust supports: Rust! So, port multirust to Rust.

Then, it was decided that mutlirust-rs would be the right path to move forward generally, so a plan was formed to figure out just exactly how we'd want such a tool to truly work, rather than just copying what multirust did, and so this became rustup.

I do recommend using rustup to all Rust developers now, despite still having reservations about its done-ness, and not being ready to commit to putting it on the main website (I guess that's something of a contradiction).

This blog post marks the beginning of the phase where we will seriously try not to break things on upgrade - I consider it 'in production' now.

Even now I think it provides the best installation experience and I have much higher confidence in its reliability than the older multirust shell script.

That said, if you are on Windows you might want to be more cautious. Just this week I broke rustup's networking on Windows, and there are periodic reports of intermittent self update failures (though these don't cause data corruption).

This blog post is sort of like a bigger beta announcement, to get things in front of a larger audience and make sure things are still good. It will be the recommend way to install rust soon, but not quite yet.

This says that musl will build and run on Linux 2.6.x, but it says nothing of the binary compatibility between systems.

If I build musl and statically link my program to it on one version of the Linux kernel, and then I copy that to an older version of the Linux kernel (both 2.6 or greater), I'm extremely skeptical that it would just work (especially for any two arbitrary versions above 2.6).

I expected it to work for most cases - especially trivial ones like that.

Where I was skeptical was around new features added to the kernel. I do not know how careful musl is when it is built on a kernel which includes a new feature (say something like F_DUPFD_CLOEXEC, added in 2.6.24), but is then copied and run on an older kernel (2.6.10) which would return -EINVAL from that system call.

A quick glance at the musl sources shows that in this particular case musl is careful to notice the -EINVAL and emulate it (via F_DUPFD and F_SETFD FD_CLOEXEC).

But without seeing documentation from musl that this is guaranteed for everything that could be added in later kernels (I'm not even sure everything added could be emulated easily, but perhaps it could be), then I'd still be skeptical making the claim that musl and Rust could be statically linked on any version of Linux after 2.6 and run on any other version of Linux after 2.6.

It's not really about the kernel ABI being compatible (programs built on older kernels run on newer ones quite nicely). It's about newer features from newer kernels still being supported (or their absence detected and their features emulated) on older kernels. That's a property of musl, not of the kernel.

Gotcha, that does make sense. I tried looking around for more information about specifics here, but couldn't really find anything. I did think that musl was attempting to deal with this, but without something explicitly saying it, I am wondering if that's something that I misunderstood, or just heard somewhere.

First, my example was fcntl(2), which musl is emulating. So that doesn't fit your "rule".

Second, is your "rule" documented anywhere for musl? That's what I'm looking for - an indication by the musl project that such a thing is supported (binary compatibility from newer to older Linux kernels, and if so, what version range).

Without such a project-sanctioned statement, I'm afraid I stand by my position that the blog's assertion that the statically-linked rust-musl binary can be copied to any Linux 2.6.x machine (or newer) and just run without any issues.

I would agree that any statically-linked rust-musl binary could be built on a Linux kernel and then run on a later Linux kernel, but earlier, well that's up to the musl project to say.

This is definitely a big step forward. I had become spoiled by Go's cross compile capabilities, which Rust had paled in comparison to. Prior to this, it was a pain having to get the right toolchain for each platform. With this, I can download the toolchain as needed for the target platform, and build against it.

Today Rust only has a [few patches to LLVM](https://github.com/rust-lang/llvm/tree/rust). One is for Android stack overflow detection using a mechanism that upstream isn't fond of (split stacks), the other an optimization not required for correctness.

The Android patch can be eliminated someday with stack probes (though it's not clear upstream wants those either).

Emscripten support though - at least in the short term - is going to bring in the [emscripten LLVM 'fastcomp' backend](https://github.com/kripken/emscripten-fastcomp) that translates LLVM IR to JS. This patch has no hope of being upstreamed and will impose significant maintenance burden on both Rust and Emscripten as long as its in tree. This solution should be short-lived though as we will transition to either the upstream LLVM->wasm backend or a new Rust MIR->wasm backend.

We generally try to upstream our patches, and they've been generally accepted. IIRC, our current fork is very close to LLVM head. We also do support building with stock LLVM, though it may have bugs for the stuff that wasn't patched at the time that release was made, of course.

Try `rustup target add aarch64-apple-ios` and see how far you get. It's a tier 2 platform so it usually has builds available. But the iOS targets are some of the least tested for Rust. I have no idea if they work!

The process for adding tier 2 platforms isn't well defined but is closely related to ease of automation. If it can be done in a Docker container then it is simple to build std and ship it. Right now we're enthusiastic about this level of support - we can provide builds of std for lots of things. As long as somebody cares just enough to keep std building, which is pretty easy to do.

Whether those builds work at all is a different matter! We don't run tests on most tier 2 platforms. It's a big commitment to do so, even more to keep the tree green.

Personally, I really want to say that in time Rust will have perfect test and build automation on all platforms that matter even a little bit. All platforms are on a slow treadmill to perfection. They all come with maintenance burden, but the more successful the project is the more maintenance (and perfection) we can afford. Hm, I hope that's how it works...

I've done that once but since building rustc requires a specific nightly I'd need a glibc environment each time I want to build rustc. Replacing the glibc builds with a musl static build (not targeting but built with musl statically and no glibc requirement) would give us a single binary that works on Alpine and Ubuntu. If that's not an option I'd welcome a musl variant that's automatically installed by rustup when on Alpine or VoidLinux musl edition or any other musl linux environment.